but after 15 years, i am sure you willnot be able to find any devise where you can put this floppy disk to start, so they would be usless.
take some mini disk and write your wallet.dat and txt file there and put this disk in the safe place. this will be better option
I think it will be easy to find readers. There are a lot of retro stuff, you can buy a floppy disk reader that can be connected through USB... there will always be a niche market of people that need to access old data. If the ones I have now break (I doubt it because at the end of the day it's pretty simple and mechanical stuff) it should not be hard to find some reader out there.
Also the idea is that I have a bunch of floppy disks. So If I have a box with like 50 floppy disks, and I put wallet files on all 50 floppy disks, it means that I have 50+ extra different points of failure for free. I think it's very unlikely that 50 floppy disks will die in 15 years, im sure at least 1 will survive

I think that everything that yoiu can store local isbetter than when you use online wallets because i know that online wallets can be hacked.